Editor class has two difference code paths for spell-checking:
(1) checkTextOfParagraph() for Snow Leopard or later
(2) checkSpellingOfString() and checkGrammarOfString() for other platforms.
These paths should be unified so that improving spell-checking code is easy.
At the first step, we should call checkTextOfParagraph() indirectly so that we can implement a function to mimic checkTextOfParagraph() in non-SL or non-Lion platform.